Transfer factor, a dialyzable lymphocyte extract that may act as an immune stimulator by transferring antigen-specific immunity between genetically dissimilar individuals, was administered in a prospective, randomized study to patients with non-small cell bronchogenic carcinoma. Between 1976 and 1982, 63 patients who underwent pulmonary resection, mediastinal lymph node dissection, and, when indicated by the presence of mediastinal lymph node involvement, mediastinal irradiation were randomized into two groups. Group 1 (n = 28) received 1 mL of pooled transfer factor at 3-month intervals after operation; group 2 (n = 35 ) served as controls and received saline solution. There were no statistically significant differences between the two groups with respect to age, sex, tumor histology, stage of disease, or extent of resection. One patient was lost to follow-up at 96 months; follow-up was complete in all others through July 1990. In patients receiving transfer factor, the 2-, 5-, and 10-year survival rates were 82%, 64%, and 43% respectively, whereas in controls they were 63%, 43%, and 23%. Survival in patients receiving transfer factor was consistently better than in those receiving placebo. Furthermore, survival in patients receiving transfer factor was greater at all stages of disease for both adenocarcinoma and squamous cell carcinoma. Although these long-term results were not statistically significant using survival analysis with covariates (p = 0.08), they confirm our previously reported short-term findings suggesting that administration of transfer factor, either through nonspecific immune stimulation, enhancement of cell-mediated immunity, or an as yet undefined mechanism, can improve survival in patients with bronchogenic carcinoma.